1. Field of the Invention
This invention relates to a lubricating structure of an automatic transmission principally used for controlling the transmission of driving force in a vehicle.
2. Description of the Prior Art
As shown in FIGS. 4 to 6, there has been known a conventional lubricating structure of an automatic transmission as disclosed in, for example, Japanese Patent Application Early Laid-Open Publication No. Sho 62-288753. This type of conventional automatic transmission has a transmission gear device which consists of four forward gears and one reverse gear by which gear shifting is performed.
Referring to FIGS. 4 to 6, a cylindrical drum 5 is rotatably connected to a front sun gear 4 by the medium of a connecting shell 3 around an input shaft 1b in a case 2 of an automatic transmission 1.
In the drum 5, a reverse clutch device 6 and a high clutch device 7 are disposed parallel to the input shaft 1b. The reverse clutch device 6 and the high clutch device 7 are multiplate clutch devices and have a function of engaging or disengaging a multiplate clutch plate by the shoving pressure of a clutch piston so as to shift a transmission state of driving force. A clutch drum 6a of the reverse clutch device 6 is connected to the drum 5 and is rotated by the rotation of the drum 5.
A brake band 9 of a band brake device 8 is attached to the circumferential surface of the drum 5. The rotation of the drum 5 is controlled by a piston 11 of a band servo device 10 shown in FIG. 6.
In the circumferential surface of the drum 5, there is formed an oil hole 15 through which lubricating oil is supplied to a space defined between sliding surfaces of the brake band 9 and the drum 5.
In the rear of the connecting shell 3, a front planetary gear device 12 and a rear planetary gear device 13 are disposed parallel to the input shaft 1b.
A front planet carrier 14 in the front planetary gear device 12 is linked to a high clutch hub 16 in the high clutch device 7 through a cylindrical sleeve portion 17.
A rear planet carrier 18 in the rear planetary gear device 13 is linked to a front internal gear 19 in the front planetary gear device 12 and is also linked to an output shaft 20 disposed coaxially with the input shaft 1b.
For example, in the third forward gear, the high clutch device 7 is engaged whereas the band brake device 8 is disengaged. On the other hand, in the fourth forward gear, the band brake device 8 as well as the high clutch device 7 is engaged, and the drum 5 is then fixed to the transmission case 2 and thereby the front sun gear 4 is also fixed thereto.
The rotational driving force inputted by the input shaft 1b is transmitted from the high clutch device 7 to the front planet carrier 14 via the high clutch hub 16, and thereby a front planetary gear 21 is rotated around the front sun gear 4.
Accordingly, the rotation of the front internal gear 19 is accelerated, and thereby the output shaft 20 connected to the rear planet carrier 18 is rotated at a speed equal to or higher than the input shaft 1b.
Oil paths 22 and 23 are formed in the input shaft 1b and the high clutch hub 16, respectively. When the drum 5 is rotated, lubricating oil is supplied to the front planetary gear device 12 and the rear planetary gear device 13 via the oil paths 22 and 23, and is also supplied to the space defined between the sliding surfaces of the brake band 9 and the drum 5 through the oil hole 15 formed in a circumferential part of the drum 5 via the oil paths 22 and 23, the high clutch device 7, and the reverse clutch device 6.
However, in a lubricating structure of this type of automatic transmission, in the fourth forward gear, the band brake device 8, which is disposed outside of the high clutch device 7 and fixes the drum 5, is supplied with operating oil and is engaged at the same time that the high clutch device 7 is engaged.
Accordingly, the lubricating oil which has lubricated and cooled the high clutch device 7 via the oil paths 22 and 23 is discharged from the oil hole 15 and is supplied to the space between the sliding surfaces of the brake band 9 and the drum 5 without lowering its high temperature. Therefore, high cooling efficiency has not been obtained.
Besides, as mentioned above, the band brake device 8, which is disposed outside of the high clutch device 7 and fixes the drum 5, is supplied with operating oil and is engaged simultaneously with the engagement of the high clutch device 7. This has caused an increase in the quantity of operating oil. Moreover, since the band brake device 8 is disposed outside of the high clutch device 7, lubricating oil is dispersed when the drum 5 is rotated. This has made it difficult to supply a predetermined quantity of oil to the band brake device 8.
The band brake device 8 is engaged in the second forward gear and the fourth forward gear and is disengaged in the third forward gear. Thus, the engagement and disengagement for the gearshifting of the band brake device 8 are repeatedly carried out with high frequency of use even when ordinary acceleration is carried out (for example, when the gear is shifted in sequence of the first gear, the second gear, the third gear, and the fourth gear). Accordingly, there has been a fear that production costs may be raised because friction materials superior in heat-resisting property must be used for the sliding surfaces of the brake band 9 and the drum 5 if sufficient cooling cannot be expected.
As a result of disposing the band brake device 8 outside of the drum 5 as shown in FIG. 6, a given space cannot be utilized efficiently. Furthermore, the band brake device 8 is constructed of relatively large parts, such as the brake band 9, the band servo device 10, and the like. For this reason, an increase in the number of the assembly parts leads to a raise in production costs and to an increase in the weight of the assembly parts.